Problems installing MESHmachine Add-on
Do NOT extract the zip file of a downloaded add-on unless told otherwise in the installation instructions!


Instead, just go to "User Preferences - Add-ons" and use the "Install Add-on from file" button. Navigate to the folder to which you downloaded the add-on, double-click on the zip file and activate the add-on.


Do NOT try to install add-ons in Blender 2.80 that aren't made specifically for Blender 2.80!


If the instructions tell you, that an add-on is not yet ready to be used in Blender 2.80, it means exactly that.*

Instead, use the Blender version that is required for the add-on to work. 

How to clean up your messed-up installation

Exit Blender, then go to your "Blender\2.xx\scripts\addons" folder and delete the folder/script. Start Blender and check "User Preferences - Add-ons" and look for the add-on. It should be gone. 

*In your case, MESHmachine does not support Blender 2.80 yet.